The long term goal of this research is to increase understanding of the normal physiological mechanisms by which nerve cells communicate with their targets. A major emphasis of this proposal is on studying the physiological roles of neuropeptides. It is widely suspected that neuropeptides play a significant role in long term regulation of neural signalling. However, although there is a significant amount of knowledge about the anatomical distribution and pharmacological actions of neuropeptides, there is a relatively little knowledge about the presynaptic mechanisms by which neuropeptides are released or about the postsynaptic actions by which synaptically released neuropeptides act upon their target cells. Neurons dissociated from the myenteric plexus of the rat provide a simplified system in which to test the functional role of several neuroactive molecules. Neurons in these cultures contain many of the major identified neuropeptides and they form several types of functional synapses. A unique feature of this particular culture system is that it permits the study of peptide-mediated synaptic events. For example, about 10% of the cholinergic neurons in these cultures contain immunoreactive (IR) VIP and can cause both fast cholinergic and slow, non- cholinergic synaptic potentials. Other populations of the cultured neurons, among them those that contain IR-Substance P, also have non- cholinergic synaptic actions. The specific aims for this proposal are to take advantage of this culture system by using a combination of electrophysiological, immunological, biochemical and pharmacological methods: 1. To continue to identify molecules that mediate slow synaptic events. 2. To investigate the cellular and biophysical mechanisms by which enteric neurons release slow transmitters and to compare them to the mechanisms by which ACh is released. 3. To investigate biophysical and molecular mechanisms by which slow synaptic potentials are generated in enteric neurons. 4. To investigate molecular and biophysical mechanisms of presynaptic modulation of release of fast and slow transmitters by enteric neurons. One specific health-related feature of this research is that one of the agents that modulates transmitter release in these cultures is the ubiquitous inflammatory agent platelet activating factor. Improved understanding of interactions between mediators of inflammation and release of bioactive peptides from nerve terminals could potentially lead to significant new lines of treatment of inflammation of the gastrointestinal tract. However, the major health-relatedness of this work is that better understanding of normal physiological processes is necessary for understanding how these processes go awry in disease. Such understanding may lead to the design, testing and development of better, more specific, treatments of perturbations of neural transmission caused by disease, injury or aging.